If you have a small company with 5 or 10 users, it would be very useful to have a shared index (like i.e. the softwre Lookeen), especially to reduce the network and exchange traffic and to have consistent search results. Because now, when you scan i.e. the same (shared) Exchange-Mailboxes with more than one client, the search result isn't every time the same on each machine. It seems that X1 has to rescan some (Mail)folders multiple times to get the final result? Maybe a bug in 8.4 beta?